docstr: Returns the rank of the Cache.
docstr_tok: ["Returns","the","rank","of","the","Cache","."]
code: def rank(self) -> int:
      """Returns the rank of the Cache."""
      if self._rank is None:
          self._worker_env = _WorkerEnv.detect()
          self._rank = (
              self._distributed_env.global_rank
              * self._worker_env.world_size
              + self._worker_env.rank
          )
      return self._rank
  
imports: import logging
  import os
  from dataclasses import dataclass
  from typing import Any, Dict, List, Optional, Tuple, Union
  from lightning.data.streaming.constants import _INDEX_FILENAME, _LIGHTNING_CLOUD_LATEST, _TORCH_GREATER_EQUAL_2_1_0
  from lightning.data.streaming.item_loader import BaseItemLoader
  from lightning.data.streaming.reader import BinaryReader
  from lightning.data.streaming.sampler import ChunkedIndex
  from lightning.data.streaming.serializers import Serializer
  from lightning.data.streaming.writer import BinaryWriter
  from lightning.data.utilities.env import _DistributedEnv, _WorkerEnv
  from lightning.data.utilities.format import _convert_bytes_to_int
label_desc: Use image node_id 2 for calling the Cache obj's underlying member method code with example usage: obj.rank() and returns: self